Heating device and control therefor



S. THOMSON.

' HEATING DEVICE AND CONTROL THEREFOR.

APPLICATION FILED FEB. 26, 1918.

Patented Aug. 24, 1920.

Stuart, Thcmson,

Invent or UNITED STATES PATENT OFFICE;

STUART THOMSON, OF WASHINGTON, DISTRICT OF COLUMBIA, ASSIGNOR TO GENERALELECTRIC COMPANY, A CORPORATION OF NEW YORK.

HEATING DEVICE AND CONTROL THEREFOR.

Specification of Letters Patent.

Patented Aug. 24, 1920.

Application filed February 26, 1918. Serial No. 219,297.

To all whom it may concern Be it known that LISTUART THOMSON, a citizenof the United States, residing at .Washington, District of Columbia,have invented certain new and useful Im rovethe unit with two separateresistance elements which were connected in series or parallel for lowor high heats, respectively, medium heat being secured by connecting asingle resistance element tothe supply circuit. The two heating unitswhich are required' for such a system of heat control, require fourterminals, and are, of course,

more expensive than a single unit and more likely to get out of order.

Another disadvantage of this system of control is that the ratios of thevarious heats, which are as 12 3:}, are not such as are usually desiredin practice. For example, the hot plates used on electric rangescommonly require for medium heat about four or five hundred watts,whereas the maximum desirable is more than twice this amount and may,for example, be 1500 watts, while it may be desirable to operate theunit at half or less than half of the wattage re uired for medium heat.

n accordance with my invention, a single resistance element is used in aheating unit.

My invention relates to an arrangement for varying the temperature of aheating unit or a heating device, comprising a transformer, preferablyan auto-transformer, and switch vmechanism associated therewith forvarying the number of turns of the secondary of the transformer whichare included in circuit with the heating unit or units. In the a waythat whenthe heating unit or units are being supplied with full heat,the autotransformer is not called upon to transmit any energy whatever,and does transmit energy only when the unit' or units are operated at alower heat, as for example medium or low heat, thereby making itpossible to use a transformer of moderate size in a heating circuit ofhigh wattage.

In another aspect, my invention relates to a three-wire alternatingcurrent system wherein the heating units each have one terminalconnected to the neutral with the auto-transformer interposed betweenthe supply circuit and the heating units, toether with an arrangementwhereby each heating unit may be connected across a supply conductor andthe neutral or across any desired number of turns of theauto-transformer, so that the auto-transformer will be called upon totransmit energy only when one or more of the heating units is connectedfor a lower heat, and when the heating units are connected for a lowerheat all of the coils of the auto-transformer are called upon totransmit energy. The most effective use is thereby made of the auto-,transformcr, and the temperature of each of the heating units is verynicely condiagrammatically illustrated, and in which Figure 1 is a vlewshowing an element of my invention Fig. 2 shows elements of my inventioncm odied in a three-wire alternating current system with anauto-transformer interposed between the heating unit, and the supplymains; and Fig; 3 shows an embodiment of my invention in a three-wirealternating current system.

Referring now to the drawings and first to Fig; 1, 10 and 11 are supplyconductors across which is connected an auto-transformer 12. Oneterminal of a heating unit 15 is connected by a conductor 14 to oneterminal of the auto-transformer, and the other terminal of the heatingunit is connected to a switch 16. This switch cooperates with contacts,here illustrated as three, 18, 19 and 20 which are connected to supplyconductor 10, to a tap 21-0n the auto-transformer and to a second tap 22ioa between the tap 21 and that terminal oil the transformer to whichthe conductor 11 is connected, respectively.

I ing unit, the switch 16 is connected to the contact 18 andthe heatingunit connected directly across the supply circuit. The auto-transformerat this time is not called upon to transmit any power. By connecting theswitch to the contact 19, the heating unit will be connected across theportion of the auto-transformer between the tap 21 and the terminal ofthe auto-transformer to which the conductor 11 is connected, a lowervoltage will be impressed on the heating device and the same willaccordingly operate at a lower heat, and by connecting the switch to thecontact 20, a still lower voltage and lowerheat will be secured. litwill be obvious that by suitably arranging the tape 21 and 22 and by theuse of additional taps, it necessary, any desired heat ratios may besecured. I

Tn Fig. 2 l have illustrated elements of my invention embodied ina'threawire al ternating current system, an auto-transformer beinginterposed-between the. supply circuit and the heating unit or units andthe units being so connected tothe autotransformer that the latter willnot transmit any energy when the heating unit or units are connected forhigh heat and will be called upon to transmit energy only when the unit.or units are connected for medium or lowheat. In this figure l haveillustrated two heating units 15 and 15*, one terminal of each of whichis connected to an intermediate tap 13 on the auto-transformer whichdivides the same into two sections 12 and 12" by a conductor 14;. Theother terminal of the heating unit 15 is connected'through switch 16 andcontacts 18-, 19 and 20, either to the conductor 10 or to extra taps 21and 22 of the auto-transformer in precisely the same manner as thedevice already described in connection with Fig. 1, while the remainingterminal of the heating unit 15" is conneeted through the switch 16 andcontacts 18, 19 and 20 eitherto the conductor 11 or to the extra tape 23and 24 of the autotransformer in precisely the same manner as thecorresponding parts associated with the unit 15.

When used in conjunction with a threewire'system, as illustrated in Fig.2, in which the neutral is indicated by the reference character 14;,then if either or both of the units are connected for high heat,

plied by the secondary of the'supply transformer (not shown in thedrawing), in'a described in connection with Fig. 2.

other two heating units, 73. e. 15 and 15 ea set manner :well understoodin the The only time when the auto-transformer will be called upon totransmit energy will be when one or both of the units is connectedto'receiv'e less than its maximum energy suppl with the consequence thatan autotrans oi'mer of moderate size may be connected in a circuit ofhigh wattage.

In Fig; 8, I have shown an embodiment of my invention in which therearetwo sets of heating units each set comprising two groups of unitsconnected to the respective sections 12 and 12 oi the auto-transformer.

The one set which is shown in the figure as will, of course, beunderstood that each group may comprise more than a single heatmg unit.The heating units 15 and 15 are connected and operated in precisely thesame .manner as the corresponding units have one terminal connected bythe conductor 14: to the tap 13 of the auto-transformer. The otherterminal of the unit 15 is connected to a switch 16- cooperating withcontacts 18, 19 and 20 and the other to a switch 16 cooperating withcontacts 18, 19 and 20, respectively. The contacts 18 and 18 areconnected to the su ply conductors 10 and 11, respectively and thecontacts 19 and 1'9 are connected to the taps 21 and 23 of theauto-transformer. The remaining contacts 20 and 20 are connect ed totaps 25 and 26 of the auto-transformer intermediate between the taps 13and 21 and the taps 13 and 22, respectively. With this arrangement hereshown, it will be apparent'that if all of the heating units areoperating at medium heat all of the difcalled upon to perform a part-hfthey work and the auto-transformer will, therefore, be moreadvantageously operated than if a part only of the coils were calledupon to transmit all the power. Similarly, if all of the heating unitsare connected for low heat, the power will be transmitted 'to theheating units by difierent coils of the auto-transformer.

While l have shown an arrangement tor securing three difierent heats ina given heating unit, it will he understood that by suitably varying thennmher of taps on the auto-transformer, and the relative numher' ofturns in the varioussections ofthe autotranstormer, any number otheatsand any desired heat'ratios. may be secured in a given heating unit.

. While T have descrihed my invention as The 110 ferent coils of theauto-transformer will be i embodying a concrete structure and asoperating in a specific manner in accordance with the provisions of thepatent statutes, it should be understood that I do not limit myinvention thereto, since various modifications thereof will suggestthemselves to those skilled in the art without departing from the spiritof my invention, the scope of which is set forth in the annexed claims.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is:

1. In combination, a supply circuit, an auto-transformer connectedthereto, a plurality of sets of heating units connected to differentsections of said auto-transformer, means for varying the energy suppliedto a given unit, each set comprising two groups of units which areconnected to different and connections for varying the number of turnsofthe auto-transformer connected in circuit with each heating unit,whereby when both units are receiving energy allthe turns of theauto-transformer will be used in transmitting power to the heatingunits.

3. The combination with a three-wire alternatingcurrent supply circuit,of two sets of heating units, the sets being connected on opposite sidesof the neutral and having one terminal of each set connected to theneutral, an auto-transformer interposed be tween the heating units andthe supply cir- "cuit, and means for connecting each heating unit acrossits associated supply conductor and the neutral or across any deslrednumber of turns of the auto-transformer, whereby the auto-transformertransmits no energy unless one or more of the units is connected for alower heat and when the units are connected for a lower heat all theturns of the auto-transformer are used in transmitting energy to theheating units.

In witness whereof I have hereunto set my hand this 20th da of Februar1918. ST ART THO SON.

